322 



"A.LBATKOSS" TROPICAL PACIFIC EXPEDITION. 



the navigation of small boats. The eastern extension of Terranova is 

 partly flanked on the lagoon side by a high sand beach, and a heavy 

 shingle beach on the sea face rising from a narrow reef flat. On the 

 lagoon side of the land rim a large part of the shore is divided into a 

 series of bays, separated by points and spits of beach rock conglomerate 

 and rolled coral boulders which have been thrown over the island, or 

 rather thrown over the reef flat forming the eastern spit, before the 



island was built up to 

 uJM^ ; its present height. The 



greatest width of the 

 secondary lagoon is one 

 and a quarter miles, and 

 its length about three 

 miles. The islands and 

 islets on the western 

 face of the northeast 

 horn of the lagoon (PI. 

 181, figs. 3, 4) are flanked 

 by coarse shingle beaches 

 on the sea face, and by sand beaches on the lagoon side. They are 

 well wooded and, as a general rule, have been built up at right angles 

 to the trend of the horn of the lagoon. The gaps between the com- 

 ponent islands and islets have, little by little, been closed from the outside 

 or the inside, according to the prevalence of the trades. The formation 

 of the secondary lagoon of the northeastern spit is easily explained by 

 the accumulation of loose material thrown up on the reef flat, derived 

 either from the eastern or the western face of the horn bounded by the 

 line of islands on the west and Terranova on the east of the lagoon. 

 This has separated the horn of tlie lagoon from the principal lagoon 

 exactly as the secondary lagoon of the northeast point has been separated 

 from the northeast horn of the main lagoon. 



The northeast horn of the lagoon is undoubtedly gradually filling up ; 

 a number of coral patches, sand bars, and spits will little by little encroach 

 upon the lagoon, the depth of wliich is at present very considerable, 



BoiiLDKR Cusps, ]j.4goon Face ok Noiitueast Spit. 

 Arhxij. 



